Angiogenesis is a key step in tumor growth and metastasis. The mechanism by which osteopontin (OPN) induces the angiogenesis of endothelial cells remains unclear. Here, we show that OPN confers cytoprotection through the activation of the PI3K/Akt pathway with subsequent upregulation of Bcl-xL and activation of nuclear factor-kappaB. OPN enhances the expression of vascular endothelial growth factor (VEGF) through the phosphorylation of AKT and extracellular signal-regulated kinase (ERK). In turn, OPN-induced VEGF activates PI3K/AKT and the ERK1/2 pathway as a positive feedback signal. Blocking the feedback signal by anti-VEGF antibody, PI3-kinase inhibitor or ERK inhibitor can partially inhibit the OPN-induced human umbilical vein endothelial cell (HUVEC) motility, proliferation and tube formation, while blocking the signal by anti-OPN or anti-alphavbeta3 antibody completely abrogates the biological effects of OPN on HUVECs. In addition, blood vessel formation is also investigated in vivo. The antiangiogenesis efficacy of anti-OPN antibody in vivo is more effective than that of anti-VEGF antibody, which only blocks the feedback signals. These data show that OPN enhances angiogenesis directly through PI3K/AKT- and ERK-mediated pathways with VEGF acting as a positive feedback signal. The results suggest that OPN might be a valuable target for developing novel antiangiogenesis therapy for treatment of cancer.

Accumulating evidence has demonstrated that myeloid-derived suppressor cells (MDSCs), a heterogeneous population of cells, play an important role in the subversion, inhibition, and downregulation of the immune response to cancer. However, the characteristics of these cells, particularly clinical relevance, in malignant tumors remain unclear due to a lack of specific markers. In this study, we characterized peripheral CD14(+)HLA-DR(-/low) cells, a new human MDSC subpopulation, in 89 patients with non-small cell lung cancer (NSCLC). As expected, both frequency and absolute number of CD14(+)HLA-DR(-/low) cells were significantly increased in the peripheral blood of NSCLC patients compared with that of the healthy controls and indicated an association with metastasis, response to chemotherapy, and progression-free survival. These cells showed decreased expression of CD16 and CD86 compared with HLA-DR(+) monocytes. Unlike classical monocytes, these populations showed significantly decreased allostimulatory activity and showed the ability to inhibit autologous T cell proliferation and IFN-γ production in a cell-contact-dependent manner. Furthermore, we demonstrated that CD14(+)HLA-DR(-/low) cells expressed the NADPH oxidase component gp91(phox) and generated high level of reactive oxygen species (ROS). Moreover, inactivation of ROS reversed their immunosuppressive capacity on T cell response. These results prove, for the first time, the existence of ROS-producing CD14(+)HLA-DR(-/low) myeloid-derived suppressor cells in NSCLC patients, which mediate tumor immunosuppression and might thus represent a potential target for therapeutic intervention.

There is an urgent need for improved therapy for advanced ovarian carcinoma, which may be met by administering immune-modulatory monoclonal antibodies (mAbs) to generate a tumor-destructive immune response. Using the ID8 mouse ovarian cancer model, we investigated the therapeutic efficacy of various mAb combinations in mice with intraperitoneal (i.p.) tumor established by transplanting 3 × 106 ID8 cells 10 days previously. While most of the tested mAbs were ineffective when given individually or together, the data confirm our previous finding that 2 i.p. injections of a combination of anti-CD137 with anti-PD-1 mAbs doubles overall survival. Mice treated with this mAb combination have a significantly increased frequency and total number of CD8+ T cells both in the peritoneal lavage and spleens, and these cells are functional as demonstrated by antigen-specific cytolytic activity and IFN-γ production. While administration of anti-CD137 mAb as a single agent similarly increases CD8+ T cells, these have no functional activity, which may be attributed to up-regulation of co-inhibitory PD-1 and TIM-3 molecules induced by CD137. Addition of the anti-cancer drug cisplatin to the 2 mAb combination increased overall survival >90 days (and was probably curative) by a mechanism which included a systemic CD8+ T cell response with tumor specificity and immunological memory. Strikingly, combined treatment of cisplatin and CD137/PD-1 mAb also gave rise to the long-term survival of mice with established TC1 lung tumors. A similar combination of the 2 mAbs and cisplatin should be considered for clinical ‘translation’.